The invention relates to a multi-channel record/playback magnetic head, and more particularly, to such a head which may be used in a magnetic recorder of the vertical magnetization type in which a high density recording is achieved by establishing a remanence in the direction of thickness of a magnetic recording medium such as magnetic tape.
Ordinarily, the technique to record an information signal on a magnetic recording medium such as magnetic tape comprises bringing a magnetic head into abutment against the surface of the medium to establish a remanence in a direction parallel to the surface of the medium. As is well known, when this technique is used, the head has its poles located opposite to each other with a narrow air gap therebetween so that a leakage flux from the gap is bypassed through the medium. Because the leakage flux passes through the medium in a direction parallel to its surface, the magnetizable material contained in the medium is magnetized in a direction parallel to the surface of the medium, with its remanence defining a magnetic record. With the described magnetic recording technique, it is known that considerations of the air gap of the magnetic head and the frequency of signals being recorded impose a limitation on the recording density of information signal.
Recently, a variety of recording techniques have been proposed which drastically improves the recording density by a so-called vertical magnetization scheme in which a remanence is established in the medium in a direction perpendicular to the surface thereof or in the direction of its thickness. This technique employs a magnetic recording medium having an easy axis of magnetization in a direction perpendicular to the surface. Referring to FIG. 1, there is shown a magnetic recording medium 6 comprising a base film 6c of polyester, for example, carrying an upper layer 6b of high permeability material and a top layer 6a coated thereon which is formed of a magnetizable material having an easy axis of magnetization in a direction perpendicular to the surface.
FIG. 1 also shows a magnetic head 1 which may be used for recording a signal in such medium. Head 1 shown is adapted to record a signal on or reproduce a signal from one track. It comprises a magnetic head core 2 of a magnetizable material such as ferrite which has an inverted U-configuration and a coil 3 disposed thereon. The core 2 has a pair of limbs 4, 5, the free end of which define magnetic poles 4a, 5a which may be brought close to or in abutment against the magnetic recording medium 6 for purpose of recording and/or playback. In use, when a signal current is passed through coil 3 while disposing the poles 4a, 5a of the head 1 close to or in abutment against the top layer 6a of the recording medium 6 and moving the medium in a direction perpendicular to the plane of the drawing, a recording flux 7 is produced within the core 7. The flux leaving the pole 4a passes through the top layer 6a perpendicularly and then passes through the high permeability layer 6b horizontally or in a direction parallel to the surface and then returns to the pole 5a, thus forming a closed magnetic path. Since the flux passes through portions of the top layer 6a which are located opposite to the poles 4a, 5a in a direction perpendicular thereto, these portions are magnetized in a vertical direction. It will be noted that these portions are magnetized in mutually opposite directions, and the pair of magnetized portions define a desired record of the signal.
During the playback operation, as the medium 6 runs in a direction perpendicular to the plane of the drawing, the remanence formed therein produces a flux which follows a closed magnetic path including the high permeability layer 6b and the core 2 which is disposed close to or in abutting relationship therewith. The flux links with the coil 3 to produce a playback current therein which varies with time in a manner corresponding to a change with time in the remanence recorded in the top layer 6a as the medium 6 moves.
It will be evident from FIG. 1, that one track is defined by those regions of the medium 6 which are scanned by the pair of poles 4a, 5a and an intermediate region located therebetween, and that a doubled signal recording occurs because the same signal is located in those portions of medium 6 located immediately adjacent to the both poles 4a, 5a. Thus, this recording technique is wasteful in that non-used region remains, and this stands in the way to achieving a high density recording. Another disadvantage of the head 1 shown is the difficulty to maintain an accurate tracking of the poles 4a, 5a with respect to a record track, presenting a liability that undesirable signals other than the intended signal may be picked up as noises.
As mentioned previously, the track width is defined by the pair of poles 4a, 5a, and cannot be reduced inasmuch as reduction of the pole areas as well as the distance therebetween is limited by considerations of the properties of a magnetizable material. Hence it will be very difficult, if not impossible, to construct a multi-channel record/playback head of vertical magnetization type in a small construction utilizing the arrangement as illustrated in FIG. 1. Specifically, the core cannot be minimized in size for the reason mentioned above. Additionally, if a plurality of magnetic head elements, each comprising such core and a coil disposed thereon, are disposed adjacent to each other in alignment with a crosswise dimension of the recording medium, the spacing between adjacent elements must be increased in order to prevent a crosstalk between them, resulting in a degraded efficiency of utilizing the medium and an increased size of the overall head assembly. These structural disadvantages will be remarkably manifest to prohibit a practical use with an increased number of such head elements which may be required in a head assembly which is used to process a digital signal for entry and retrieval of data with a computer or which may be used in a multi-channel tape recorder of automatic reverse type.
The present applicant has previously proposed an improved construction shown in FIG. 2 and disclosed in copending U.S. application Ser. No. 020,922, filed Mar. 15, 1979, assigned to a common assignee in order to eliminate the described disadvantages of the conventional head 1. Magnetic head 11 shown in FIG. 2 comprises a magnetic head core 12 formed of a magnetizable material such as ferrite, and a coil 13 disposed thereon. The core 12 includes a magnetic record/playback limb 14 and a flux conducting, magnetic limb 15 of an inverted L-configuration which is connected with the limb 14 by a horizontal arm. It will be noted that the free end of the limb 14 is disposed opposite to the surface of the recording medium 6 to define a magnetic pole 14a which is used to record a signal on the medium or to read information therefrom. On the other hand, the free end of the limb 15 is disposed in opposing relationship with one lateral end face 6d of the medium 6 and defines a pole 15a which is adapted to conduct a flux that has passed through the high permeability layer 6b.
When the head 11 is disposed as shown so that the pole 14a is located close to or in abutment against the top layer 6a of the medium 6 and the latter run in a direction perpendicular to the plane of the drawing while passing a signal current through coil 13, a recording flux 17 is produced within the core 12, which follows a closed magnetic path including the high permeability layer 6b. The flux passes through a portion of the top layer 6a which is located opposite to the pole 14a in a perpendicular direction, thus magnetizing it in the direction of its thickness. After passing through the high permeability layer 6b, the flux returns to the core 12 from the lateral end face 6d of the medium 6, thus virtually leaving no influence upon the medium 6 other than recording the signal. It will be readily apparent that the recorded signal can be reproduced in the same manner as mentioned above in connection with FIG. 1.
When the head 11 is used, one signal track is defined by a region of the medium 6 which is scanned by the single pole 14a. Since the width of the pole 14a defines the signal track, it is unnecessary to reduce the overall size of the head core 12 as required in the arrangement of FIG. 1 in order to reduce the track width. Additionally, there occurs no wasteful signal recording on the medium 6. By reducing the width of the pole 14a, the signal track may be reduced to any desired width. Thus it will be understood that a simple construction for a multi-channel record/playback head of vertical magnetization type can be obtained by utilizing the construction of head 11.